Device, system and method for color display

ABSTRACT

A color Liquid Crystal Display (LCD) device for displaying a color image using at least four different primary colors, the device including an array of Liquid Crystal (LC) elements, driving circuitry adapted to receive an input corresponding to the color image and to selectively activate the LC elements of the LC array to produce an attenuation pattern corresponding to a gray-level representation or the color image, and an array of color sub-pixel filter elements juxtaposed and in registry with the array of LC elements such that each color sub-pixel filter element is in registry with one of the LC elements, wherein the array of color sub-pixel filter elements comprises at least four types of color sub-pixel filter elements, which transmit light of the at least four primary colors, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 10/480,280, filed Dec. 11, 2003, now U.S. Pat. No.7,268,757 which is a National Phase Application of PCT InternationalApplication No. PCT/IL02/00452, International Filing Date Jun. 11, 2002,claiming priority of U.S. Provisional Patent Application, 60/296,767,filed Jun. 11, 2001, U.S. Provisional Patent Application, 60/318,626,filed Sep. 13, 2001, and U.S. Provisional Patent Application,60/371,419, filed Apr. 11, 2002, all of which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The invention relates generally to color display devices, systems andmethods and, more particularly, to display devices, systems and methodshaving improved color image reproduction capability.

BACKGROUND OF THE INVENTION

Standard computer monitors and TV displays are typically based onreproduction of three, additive, primary colors (“primaries”), forexample, red, green, and blue, collectively referred to as RGB.Unfortunately, these monitors cannot display many colors perceived byhumans, since they are limited in the range of color they are capable ofdisplaying. FIG. 1A schematically illustrates a chromaticity diagram asis known in the art. The closed area in the shape of a horseshoerepresents the chromaticity range of colors that can be seen by humans.However, chromaticity alone does not fully represent all visible colorvariations. For example, each chromaticity value on the two-dimensionalchromaticity plane of FIG. 1A may be reproduced at various differentbrightness levels. Thus, a full representation of the visible colorspace requires a three dimensional space including, for example, twocoordinates representing chromaticity and a third coordinaterepresenting brightness. Other three dimensional space representationsmay also be defined. The points at the border of the horseshoe diagramin FIG. 1A, commonly referred to as “spectrum locus”, correspond tomonochromatic excitations at wavelengths ranging, for example, from 400nm to 780 nm. The straight line “closing” the bottom of the horseshoe,between the extreme monochromatic excitation at the longest and shortestwavelengths, is commonly referred to as “the purple line”. The range ofcolors discernible by the human eye, represented by the area of thehorseshoe diagram above the purple line, at varying brightness levels,is commonly referred to as the color gamut of the eye. The dottedtriangular area of FIG. 1A represents the range of colors that arereproducible by a standard RGB monitor.

There are many known types of RGB monitors, using various displaytechnologies, including but not limited to CRT, LED, plasma, projectiondisplays, LCD devices and others. Over the past few years, the use ofcolor LCD devices has been increasing steadily. A typical color LCDdevice is schematically illustrated in FIG. 2A. Such a device includes alight source 202, an array of liquid crystal (LC) elements (cells) 204,for example, an LC array using Thin Film Transistor (TFT) active-matrixtechnology, as is known in the art. The device further includeselectronic circuits 210 for driving the LC array cells, e.g., byactive-matrix addressing, as is known in the art, and a tri-color filterarray, e.g., a RGB filter array 206, juxtaposed the LC array. Inexisting LCD devices, each full-color pixel of the displayed image isreproduced by three sub-pixels, each sub-pixel corresponding to adifferent primary color, e.g., each pixel is reproduced by driving arespective set of R, G and B sub-pixels. For each sub-pixel there is acorresponding cell in the LC array. Back-illumination source 202provides the light needed to produce the color images. The transmittanceof each of the sub-pixels is controlled by the voltage applied to thecorresponding LC cell, based on the RGB data input for the correspondingpixel. A controller 208 receives the input RGB data, scales it to therequired size and resolution, and adjusts the magnitude of the signaldelivered to the different drivers based on the input data for eachpixel. The intensity of white light provided by the back-illuminationsource is spatially modulated by the LC array, selectively attenuatingthe light for each sub pixel according to the desired intensity of thesub-pixel. The selectively attenuated light passes through the RGB colorfilter array, wherein each LC cell is in registry with a correspondingcolor sub-pixel, producing the desired color sub-pixel combinations. Thehuman vision system spatially integrates the light filtered through thedifferent color sub-pixels to perceive a color image.

U.S. Pat. No. 4,800,375 (“the '375 patent”), the disclosure of which isincorporated herein by reference in its entirety, describes an LCDdevice including an array of LC elements juxtaposed in registry with anarray of color filters. The filter array includes the three primarycolor sub-pixel filters, e.g., RGB color filters, which are interlacedwith a fourth type of color filter to form predetermined repetitivesequences. The various repetitive pixel arrangements described by the'375 patent, e.g., repetitive 16-pixel sequences, are intended tosimplify pixel arrangement and to improve the ability of the displaydevice to reproduce certain image patterns, e.g., more symmetrical linepatterns. Other than controlling the geometric arrangement of pixels,the '375 patent does not describe or suggest any visual interactionbetween the three primary colors and the fourth color in the repetitivesequences.

LCDs are used in various applications. LCDs are particularly common inportable devices, for example, the small size displays of PDA devices,game consoles and mobile telephones, and the medium size displays oflaptop (“notebook”) computers. These applications require thin andminiaturized designs and low power consumption. However, LCD technologyis also used in non-portable devices, generally requiring larger displaysizes, for example, desktop computer displays and TV sets. Different LCDapplications may require different LCD designs to achieve optimalresults. The more “traditional” markets for LCD devices, e.g., themarkets of battery-operated devices (e.g., PDA, cellular phones andlaptop computers) require LCDs with high brightness efficiency, whichleads to reduced power consumption. In desktop computer displays, highresolution, image quality and color richness are the primaryconsiderations, and low power consumption is only a secondaryconsideration. Laptop computer displays require both high resolution andlow power consumption; however, picture quality and color richness arecompromised in many such devices. In TV display applications, picturequality and color richness are generally the most importantconsiderations; power consumption and high resolution are secondaryconsiderations in such devices.

Typically, the light source providing back-illumination to LCD devicesis a Cold Cathode Fluorescent Light (CCFL). FIG. 3 schematicallyillustrates typical spectra of a CCFL, as is known in the art. Asillustrated in FIG. 3, the light source spectra include three,relatively narrow, dominant wavelength ranges, corresponding to red,green and blue light, respectively. Other suitable light sources, as areknown in the art, may alternatively be used. The RGB filters in thefilter sub-pixel array are typically designed to reproduce asufficiently wide color gamut (e.g., as close as possible to the colorgamut of a corresponding CRT monitor), but also to maximize the displayefficiency, e.g., by selecting filters whose transmission curvesgenerally overlap the CCFL spectra peaks in FIG. 3. In general, for agiven source brightness, filters with narrower transmission spectraprovide a wider color gamut but a reduced display brightness, and viceversa. For example, in applications where power efficiency is a criticalconsideration, color gamut width may often be sacrificed. In certain TVapplications, brightness is an important consideration; however, dullcolors are not acceptable.

FIG. 4A schematically illustrates typical RGB filter spectra of existinglaptop computer displays. FIG. 4B schematically illustrates achromaticity diagram representing the reproducible color gamut of thetypical laptop spectra (dashed-triangular area in FIG. 4B), as comparedwith an ideal NTSC color gamut (dotted triangular area in FIG. 4B). Asshown in FIG. 4B, the NTSC color gamut is significantly wider than thecolor gamut of the typical laptop computer display and therefore, manycolor combinations included in the NTSC gamut are not reproducible bythe typical color laptop computer display.

SUMMARY OF THE INVENTION

Many colors seen by humans are not discernible on standardred-green-blue (RGB) monitors. By using a display device with more thanthree primary colors, the reproducible color gamut of the display isexpanded. Additionally or alternatively, the brightness level producedby the display may be significantly increased. Embodiments of thepresent invention provide systems and methods of displaying color imageson a display device, for example, a thin profile display device, such asa liquid crystal display (LCD) device, using more than three primarycolors.

An aspect of the invention provides improved multi-primary displaydevices using more than three sub-pixels of different colors to createeach pixel. In embodiments of this aspect of the invention, the use offour to six (or more) different color sub-pixels, per pixel, allows fora wider color gamut and higher luminous efficiency. In some embodiments,the number of sub-pixels per pixel and the color spectra of thedifferent sub-pixels may be optimized to obtain a desired combination ofa sufficiently wide color gamut, sufficiently high brightness, andsufficiently high contrast.

In some embodiments of the invention, the use of more than three primarycolors may expand the reproducible color gamut of the display byenabling the use of relatively narrow wavelength ranges for some of theprimary colors, e.g., red, green and blue, thus increasing thesaturation of those primary colors. To compensate for a potentiallyreduced brightness level from such narrower ranges, in some embodimentsof the invention, broad wavelength range primary colors, e.g.,specifically designed yellow and/or cyan, may be used in addition to thenarrow wavelength range colors, thus increasing the overall brightnessof the display. In further embodiments of the invention, additionalprimary colors (e.g., magenta) and/or different primary color spectramay be used to improve various other aspects of the displayed image. Inaccordance with embodiments of the invention, an optimal combination ofcolor gamut width and over-all display brightness can be achieved, tomeet the requirements of a given system, by designing specific primarycolors and sub-pixel arrangements.

The color gamut and other attributes of a more-than-three primary colorLCD device in accordance with embodiments of the invention may becontrolled by controlling the spectral transmission characteristics ofthe different primary color sub-pixel filter elements used by thedevice. According to an aspect the invention, four or more differentprimary color sub-pixel filters are used, to produce four or more,respective, primary colors, for example, RCB and yellow (Y). In furtherembodiments of the invention, at least five different primary colorsub-pixel filters are used, for example, RGB, Y and cyan (C) filters. Inadditional embodiments of the invention, at least six different primarycolor sub-pixel filters are used, for example, RGB, Y, C and magenta (M)filters.

The primary color sub-pixel filters for a more-than-three primary colorLCD device in accordance with the invention may be selected inaccordance with various criteria, for example, to establish sufficientcoverage of a desired color gamut, to maximize the brightness level thatcan be produced by the display, and/or to adjust the relativeintensities of the primary colors according to a desired chromaticitystandard.

Further embodiments of the invention provide sequential color displaydevices, systems and methods, for example, sequential color LCD devices,using more than three primary colors. In such devices, color images areproduced by sequentially back-illuminating an array of Liquid Crystal(LC) cells with light of four or more, pre-selected, primary colors,producing a periodic sequence of four or more, respective, primary colorimages, which are temporally integrated into a full color image by aviewer's vision system. In some embodiments, sequentialback-illumination with four or more primary colors is produced bysequentially filtering light through four or more, respective, colorfilters. In other embodiments, a multi-color light source, for example,a plurality of light emitting diodes (LEDs) capable of separatelyproducing any of the four or more primary colors, is activated tosequentially produce the different primary color back-illumination.

In accordance with embodiments of an aspect of the invention, there isthus provided a color Liquid Crystal Display (LCD) device for displayinga color image using at least four different primary colors, the deviceincluding an array of Liquid Crystal (LC) elements, driving circuitryadapted to receive an input corresponding to the color image and toselectively activate the LC elements of the LC array to produce anattenuation pattern corresponding to a gray-level representation of thecolor image, and an array of color sub-pixel filter elements juxtaposedand in registry with the array of LC elements such that each colorsub-pixel filter element is in registry with one of the LC elements,wherein the array of color sub-pixel filter elements includes at leastfour types of color sub-pixel filter elements, which transmit light ofthe at least four primary colors, respectively.

In accordance with embodiments of another aspect of the invention, thereis provided a color Liquid Crystal Display (LCD) device for displaying atemporally-integrated color image including a sequence of at least fourprimary color images, the device including an array of Liquid Crystal(LC) elements, driving circuitry adapted to receive an inputcorresponding to each of the at least four primary color images and toselectively activate the LC elements of the LC array to produce anattenuation pattern corresponding to a gray-level representation of eachof the at least four primary color images, respectively, and anillumination system adapted to sequentially back-illuminate the LC arraywith light of at least four different primary colors to sequentiallyproduce the at least four, respective, primary color images, wherein thedriving circuitry and the illumination system are synchronized such thateach the attenuation pattern is illuminated with light of the primarycolor corresponding to the respective primary color image.

In some embodiments of this aspect of the invention, the illuminationsystem includes a light source having an output path, a filter switchingmechanism which sequentially interposes at least four different primarycolor filters in the output path of the light source to produce thelight of at least four different primary colors, respectively, and anoptical arrangement which guides the light of at least four differentprimary colors from the filter switching mechanism to the LC arraythereby to back-illuminate the LC array. In other embodiments of thisaspect of the invention, the illumination system includes an array ofLight Emitting Diodes (LEDs), illumination control circuitry adapted toselectively activate the plurality of LEDs to produce a sequence of atleast four illumination patterns corresponding to the light of at leastfour different primary colors, respectively, and an optical arrangementwhich causes the at least four illumination patterns produced by thearray of LEDs to back-illuminate the LC array with a generally spatiallyhomogeneous light of the at least four, respective, primary colors.

In accordance with embodiments of a further aspect of the invention,there is provided a color display device for displaying an n-primaryimage, wherein n is greater than three, having an array of colorsub-pixel elements including sub-pixel elements of each of at least fourdifferent primary colors arranged in an array of periodically repetitivesuper-pixel structures covering substantially the entire n-primaryimage, each super-pixel structure including a predetermined, fixed,number of n-primary pixels, each n-primary pixel including one colorsub-pixel element of each of the at least four different primary colors,wherein no fixed combination of n-primary pixels covering only part ofthe super-pixel structure can be periodically repeated to coversubstantially the entire n-primary image.

In some embodiments of this aspect of the invention, the at least fourprimary colors include at least five primary colors, and the super pixelstructure includes a substantially rectangular arrangement includingfive sequences of four sub-pixel elements, each sequence including adifferent combination of sub-pixel elements of four of the five primarycolors. In other embodiments of this aspect of the invention, the atleast four primary colors include at least six primary colors, and thesuper pixel structure includes a substantially rectangular arrangementincluding three sequences of four sub-pixel elements, each sequenceincluding a different combination of sub-pixel elements of four of thesix primary colors.

In accordance with embodiments of an additional aspect of the invention,there is provided a method of displaying an n-primary color image,wherein n is greater than three, on an n-primary color display having anarray of color sub-pixel elements including sub-pixel elements of eachof at least four different primary colors arranged in an array ofperiodically repetitive super-pixel structures covering substantiallythe entire n-primary image, each super-pixel structure including apredetermined, fixed, number of n-primary pixels, each n-primary pixelincluding one color sub-pixel element of each of the at least fourdifferent primary colors, wherein no fixed combination of n-primarypixels covering only part of the super-pixel structure can beperiodically repeated to cover substantially the entire n-primary image,the method including receiving an input representing three-componentcolor image data, e.g., RGB or YCC data, including a plurality ofthree-component pixels and having a first resolution, scaling thethree-component color image data to produce scaled three-component colorimage data having a second resolution different from the firstresolution, converting the scaled three-component color image data intocorresponding n-primary color pixel data representing the n-primarycolor image, and generating an n-primary input signal corresponding tothe n-primary color pixel data.

In some embodiments of this aspect of the invention, the methodincludes, before generating the n-primary input signal, collecting then-primary color pixel data of all n-primary pixels of each super-pixel,and distributing the collected data representing each super-pixelstructure into a plurality of sub-pixel data segments, each segmentrepresenting one sub-pixel of each the super-pixel, wherein generatingthe n-primary input signal includes generating a gray-level value foreach of the sub-pixels.

In accordance with embodiments of yet another aspect of the invention,there is provided a method of displaying an n-primary image, wherein nis greater than or equal to six, on an n-primary display having an arrayof color sub-pixel elements including color sub-pixel elements of eachof at least six different primary colors, including at least a first setof primary colors and a second set of primary colors, arranged in aperiodically repeating arrangement including at least one colorsub-pixel element of each of the at least six different primary colors,the method including receiving an image input representing image dataincluding a plurality of pixels, each pixel including one sub-pixel ofeach of the first set of primary colors, separating the image data intoa first image component, including a first group of the pixels, and asecond image component, including a second group of the pixels, whereineach pixel in the first group is substantially adjacent to a respectivepixel in the second group, converting the pixels in the second groupinto corresponding, converted pixels, each pixel including one sub-pixelof each of the second set of primary colors, and generating an n-primaryinput signal representing data corresponding to each of the convertedcolor pixels in the second group and the respective, substantiallyadjacent, pixel in the first group.

In some embodiments of this aspect of the invention, the methodincludes, before generating the n-primary input signal, combining eachof the converted pixels in the second group with the respective,substantially adjacent, pixel of the first group, to produce acorresponding n-primary pixel including one sub-pixel of each of the atleast six primary colors, wherein generating the n-primary input signalincludes generating a signal representing data corresponding to each then-primary pixel.

Further, in some embodiments of this aspect of the invention, the imageinput includes a color image input representing three-component colorimage data, e.g., RGB or YCC data, wherein the at least first and secondsets of primary colors include first and second sets of three primarycolors, and wherein each color pixel of the n-primary image isreproduced by either the first or second set of three primary colors. Inother embodiments of this aspect of the invention, the image inputincludes a black-and-white image input representing black-and-whiteimage data including a plurality of black-and-white pixels. The at leastfirst and second sets of primary colors may include first and secondsets of three, complementary, primary colors, and each black-and-whitepixel of the n-primary image may be produced by either the first orsecond set of primary colors. Alternatively, the at least first andsecond sets of primary colors include first, second and third pairs ofcomplementary primary colors, and each black-and-white pixel of then-primary image is produced by one of the first, second and third pairsof primary colors.

In accordance with embodiments of a still further aspect of theinvention, there is provided a color display device for displaying ann-primary image, wherein n is greater than or equal to six, having anarray of color sub-pixel elements including color sub-pixel elements ofeach of at least six different primary colors, including at least afirst set of primary colors and a second set of primary colors, arrangedin a periodically repeating arrangement including at least one colorsub-pixel element of each of the at least six different primary colors,wherein each sub-pixel in the periodically repeating arrangement isadjacent at least one sub-pixel of a complementary primary color.

In some embodiments of this aspect of the invention, the periodicallyrepeating arrangement includes a first sequence of sub-pixel elements ofeach of the first set of primary colors and a second sequence ofsub-pixel elements of each of the second set of primary colors, whereineach sub-pixel element in the first sequence is adjacent a sub-pixelelement of a complementary primary color in the second sequence.

In accordance with embodiments of yet an additional aspect of theinvention, there is provided a system for displaying an n-primary colorimage, wherein n is greater than three, including an n-primary colordisplay device having an array of color sub-pixel elements includingsub-pixel elements of each of at least four different primary colorsarranged in an array of periodically repetitive super-pixel structurescovering substantially the entire n-primary image, each super-pixelstructure including a predetermined, fixed, number of n-primary pixels,each n-primary pixel including one color sub-pixel element of each ofthe at least four different primary colors, wherein no fixed combinationof n-primary pixels covering only part of the super-pixel structure canbe periodically repeated to cover substantially the entire n-primaryimage, means for receiving an input representing three-component colorimage data, e.g., RGB or YCC data, including a plurality ofthree-component pixels and having a first resolution, a scaling unit,which scales the three-component color image data to produce scaledthree-component color image data having a second resolution differentfrom the first resolution, a converter which converts the scaledthree-component color image data into corresponding n-primary colorpixel data representing the n-primary color image, and means forgenerating an n-primary input signal corresponding to the n-primarycolor pixel data.

In some embodiments of this aspect of the invention, the system furtherincludes a collection unit, which collects the n-primary color pixeldata of all n-primary pixels of each super-pixel, and a distributionunit, which distributes the collected data representing each super-pixelstructure into a plurality of sub-pixel data segments, each segmentrepresenting one sub-pixel of each the super-pixel, wherein the meansfor generating the n-primary input signal generates a gray-level valuefor each of the sub-pixels.

In accordance with embodiments of still another aspect of the invention,there is provided a system for displaying an n-primary image, wherein nis greater than or equal to six, including an n-primary display devicehaving an array of color sub-pixel elements including color sub-pixelelements of each of at least six different primary colors, including atleast a first set of primary colors and a second set of primary colors,arranged in a periodically repeating arrangement including at least onecolor sub-pixel element of each of the at least six different primarycolors, an image collector which receives an image input representingimage data including a plurality of pixels, each pixel including onesub-pixel of each of the first set of primary colors, means forseparating the color image data into a first image component, includinga first group of the pixels, and a second image component, including asecond group of the pixels, wherein each pixel in the first group issubstantially adjacent to a respective pixel in the second group, meansfor converting the pixels in the second group into corresponding,converted pixels, each pixel including one sub-pixel of each of thesecond set of primary colors, and means for generating an n-primaryinput signal representing data corresponding to each of the convertedcolor pixels in the second group and the respective, substantiallyadjacent, pixel in the first group.

In some embodiments of this aspect of the invention, the system furtherincludes a pixel combiner which combines each of the converted colorpixels in the second group with the respective, substantially adjacent,pixel of the first group, to produce a corresponding n-primary pixelincluding one sub-pixel of each of the at least six primary colors,wherein the means for generating the n-primary input signal generates asignal representing data corresponding to each the n-primary pixel.

In embodiments of the present invention, the wavelength ranges of the atleast four primary colors or, in some embodiments, the at least five orsix primary colors, are selected to provide an optimal over-allbrightness of the displayed images. Additionally or alternatively, thewavelength ranges of the at least four primary colors are selected toprovide an optimal color gamut width of the displayed images.

In accordance with embodiments of yet another aspect of the invention,there is provided a color display device for displaying an n-primaryimage, wherein n is greater than three, having an array of colorsub-pixel elements including sub-pixel elements of each of at least fourdifferent primary colors arranged in an array of periodically repetitivesuper-pixel structures covering substantially the entire n-primaryimage, each super-pixel structure including a predetermined, fixed,number of n-primary pixels, each n-primary pixel including one colorsub-pixel element of each of the at least four different primary colors,wherein the sub-pixel elements in each super-pixel structure arearranged in a rectangular sub-array having an average aspect ratiosufficiently close to one.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be understood and appreciated more fully from thefollowing detailed description of embodiments of the invention, taken inconjunction with the accompanying drawings in which:

FIG. 1A is a schematic illustration of a chromaticity diagramrepresenting a prior art RGB color gamut, superimposed with achromaticity diagram of the color gamut of a human vision system, as isknown in the art;

FIG. 1B is a schematic illustration of a chromaticity diagramrepresenting a wide color gamut in accordance with an exemplaryembodiment of the invention, superimposed with the chromaticity diagramof FIG. 1A;

FIG. 2A is a schematic block diagram illustrating a prior art 3-primaryLCD system;

FIG. 2B is a schematic block diagram illustrating an n-primary LCDsystem in accordance with an embodiment of the invention;

FIG. 3 is a schematic graph illustrating typical spectra of a prior artCold Cathode Fluorescent Light (CCFL) source;

FIG. 4A is a schematic graph illustrating typical RGB filter spectra ofa prior art laptop computer display;

FIG. 4B is a schematic illustration of a chromaticity diagramrepresenting the color gamut reproduced by the prior art RGB filterspectra of FIG. 4A, superimposed with an ideal prior art NTSC colorgamut;

FIG. 5A is a schematic graph illustrating transmission curves of one,exemplary, filter design for a five-primary display device in accordancewith an embodiment of the invention;

FIG. 5B is schematic illustration of a chromaticity diagram representingthe color gamut of the filter design of FIG. 5A, superimposed with twoexemplary prior art color gamut representations;

FIG. 6A is a schematic graph illustrating transmission curves ofanother, exemplary, filter design for a five-primary display device inaccordance with an embodiment of the invention;

FIG. 6B is schematic illustration of a chromaticity diagram representingthe color gamut of the filter design of FIG. 6A, superimposed with twoexemplary prior art color gamut representations;

FIG. 7A is a schematic graph illustrating transmission curves of afilter design for a six-primary display device in accordance with anembodiment of the invention;

FIG. 7B is schematic illustration of a chromaticity diagram representingthe color gamut of the filter design of FIG. 7A, superimposed with twoexemplary prior art color gamut representations;

FIG. 8 is a schematic illustration of an exemplary arrangement ofsub-pixels in a four-primary display device according to embodiments ofthe invention;

FIG. 9 is a schematic illustration of an exemplary arrangement ofsub-pixels, including a super-pixel structure, in a five-primary displaydevice according to embodiments of the invention;

FIG. 10 is a schematic illustration of an exemplary arrangement ofsub-pixels, including a super-pixel structure, in a six-primary displaydevice according to embodiments of the invention;

FIG. 11 is a schematic block diagram illustrating data flow in parts ofan n-primary color display system in accordance with an embodiment ofthe invention;

FIG. 12A is a schematic illustration depicting one exemplary pixelarrangement for a six-primary color display device in accordance withembodiments of the invention;

FIG. 12B is a schematic illustration depicting another exemplary pixelarrangement for a six-primary color display device in accordance withembodiments of the invention;

FIG. 13A is a schematic illustration of an exemplary color gamut of asix-primary display in accordance with embodiments of the invention;

FIG. 13B is schematic block diagram illustrating a data flow scheme fora six-primary color display system in accordance with an exemplaryembodiment of the invention;

FIG. 14 is a schematic illustration of a sequential n-primary color LCDdevice in accordance with an exemplary embodiment of the invention; and

FIG. 15 is a schematic illustration of a chromaticity diagram of a humanvision color gamut divided into a plurality of color sub-gamut regions.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following description, various aspects of the invention aredescribed, with reference to specific embodiments that provide athorough understanding of the invention; however, it will be apparent toone skilled in the art that the present invention is not limited to thespecific embodiments and examples described herein. Further, to theextent that certain details of the devices, systems and methodsdescribed herein are related to known aspects of color display devices,systems and methods, such details may have been omitted or simplifiedfor clarity.

FIG. 1B schematically illustrates a color gamut of amore-than-three-primary display in accordance with an embodiment of theinvention, enclosed by a horseshoe diagram representing the perceivablecolor gamut of the human eye, on a chromaticity plane. The six-sidedshape in FIG. 1B represents the color gamut of a six-primary display inaccordance with an exemplary embodiment of the invention. This colorgamut is significantly wider than a typical RGB color gamut, which isrepresented by the dotted triangular shape in FIG. 1B. Embodiments ofmonitors and display devices with more than three primaries, inaccordance with exemplary embodiments of the invention, are described inU.S. patent application Ser. No. 09/710,895, entitled “Device, SystemAnd Method For Electronic True Color Display”, filed Nov. 14, 2000, inInternational Application PCT/IL01/00527, filed Jun. 7, 2001, entitled“Device, System and Method For Electronic True Color Display” andpublished Dec. 13, 2001 as PCT Publication WO 01/95544, in U.S. patentapplication Ser. No. 10/017,546, filed Dec. 18, 2001, entitled“Spectrally Matched Digital Print Proofer”, and in InternationalApplication PCT/IL02/00410, filed May 23, 2002, entitled “System andmethod of data conversion for wide gamut displays”, the disclosures ofall of which applications and publications are incorporated herein byreference.

While, in embodiments of the present invention, methods and systemsdisclosed in the above referenced patent applications may be used, forexample, methods of converting source data to primary data, or methodsof creating primary color materials or filters; in alternateembodiments, the system and method of the present invention may be usedwith any other suitable n-primary display technology, wherein n isgreater than three. Certain embodiments described in these applicationsare based on rear or front projection devices, CRT devices, or othertypes of display devices. While the following description focuses mainlyon n-primaries flat panel display devices in accordance with exemplaryembodiments of the invention, wherein n is greater than three,preferably using LCDs, it should be appreciated that, in alternateembodiments, the systems, methods and devices of the present inventionmay also be used in conjunction with other types of display and othertypes of light sources and modulation techniques. For example, it willbe appreciated by persons skilled in the art that the principles of then-primary color display device of the invention may be readilyimplemented, with appropriate changes, in CRT displays, Plasma display,Light Emitting Diode (LED) displays, Organic LED (OLED) displays andField Emissions Display (FED) devices, or any hybrid combinations ofsuch display devices, as are known in the art.

FIG. 2B schematically illustrates a more-than-three primary colordisplay system in accordance with an embodiment of the invention. Thesystem includes a light source 212, an array of liquid crystal (LC)elements (cells) 214, for example, an LC array using Thin FilmTransistor (TFT) active-matrix technology, as is known in the art. Thedevice further includes electronic circuits 220 for driving the LC arraycells, e.g., by active-matrix addressing, as is known in the art, and ann-primary-color filter array 216, wherein n is greater than three,juxtaposed the LC array. In embodiments of the LCD devices according toembodiments of the invention, each full-color pixel of the displayedimage is reproduced by more than three sub-pixels, each sub-pixelcorresponding to a different primary color, e.g., each pixel isreproduced by driving a corresponding set of four or more sub-pixels.For each sub-pixel there is a corresponding cell in LC array 214.Back-illumination source 212 provides the light needed to produce thecolor images. The transmittance of each of the sub-pixels is controlledby the voltage applied to a corresponding LC cell of array 214, based onthe image data input for the corresponding pixel. An n-primariescontroller 218 receives the input data, e.g., in RGB or YCC format,optionally scales the data to a desired size and resolution, and adjuststhe magnitude of the signal delivered to the different drivers based onthe input data for each pixel. The intensity of white light provided byback-illumination source 212 is spatially modulated by elements of theLC array, selectively controlling the illumination of each sub-pixelaccording to the image data for the sub-pixel. The selectivelyattenuated light of each sub-pixel passes through a corresponding colorfilter of color filter array 216, thereby producing desired colorsub-pixel combinations. The human vision system spatially integrates thelight filtered through the different color sub-pixels to perceive acolor image.

The color gamut and other attributes of LCD devices in accordance withembodiments of the invention may be controlled by a number ofparameters. These parameters include: the spectra of the backillumination element (light source), for example a Cold CathodeFluorescent Light (CCFL); the spectral transmission of the LC cells inthe LC array; and the spectral transmission of the color filters. In a3-primaries display, the first two parameters, namely, the spectra ofthe light source and the spectral transmission of the LC cell, aretypically dictated by system constraints and, therefore, the colors forthe filters may be selected straightforwardly to provide the requiredcalorimetric values at the “corners” of the desired RGB triangle, asshown in FIG. 1A. To maximize the efficiency of 3-primaries LCD devices,the spectral transmissions of the filters are designed to substantiallyoverlap, to the extent possible, with the wavelength peaks of the lightsource. The filters selection in 3-primary LCD devices may be basedprimarily on maximizing the overall brightness efficiency. In thiscontext, it should be noted that selecting filters having narrowerspectral transmission curves, which result in more saturated primarycolors, generally decreases the over-all brightness level of thedisplay.

For a multi-primary display with more than three primary colors, inaccordance with embodiments of the invention, an infinite number offilter combinations can be selected to substantially overlap a requiredcolor gamut. The filter selection method of the invention may includeoptimizing the filter selection according to the following requirements:establishing sufficient coverage of a desired two-dimensional colorgamut, for example, the NTSC standard gamut for wide-gamut applicationsand a “conventional” 3-color LCD gamut for higher brightnessapplications; maximizing the brightness level of a balanced white pointthat can be obtained from combining all the primary colors; andadjusting the relative intensities of the primary colors in accordancewith a desired illumination standard, e.g., the D65 white pointchromaticity standard of High Definition TV (HDTV) systems.

Embodiments of the present invention provide systems and methods ofdisplaying color images on a display device, for example, a thin profiledisplay device, such as a liquid crystal display (LCD) device, usingmore than three primary colors. A number of embodiments of the inventionare described herein in the context of an LCD device with more thanthree primary colors; wherein the number of color filters used per pixelis greater than three. This arrangement has several advantages incomparison to conventional RGB display devices. First, the n-primarydisplay device in accordance with the invention enables expansion of thecolor gamut covered by the display. Second, the device in accordancewith the invention enables a significant increase in the luminousefficiency of the display; in some cases, an increase of about 50percent or higher may be achieved, as discussed below. This feature ofthe invention is particularly advantageous for portable (e.g.,battery-operated) display devices, because increased luminous efficiencyextends the battery life and overall weight of such devices. Third, adevice in accordance with the invention enables improved graphicsresolution by efficient utilization of a sub-pixel rendering techniqueof the present invention, as described in detail below with reference tospecific embodiments of the invention.

In some multi-primary display devices in accordance with embodiments ofthe invention, more than three sub-pixels of different colors are usedto create each pixel. In embodiments of the invention, the use of fourto six (or more) different color sub-pixels, per pixel, allows for awider color gamut and higher luminous efficiency. In some embodiments,the number of sub-pixels per pixel and the transmittance spectrum of thedifferent sub-pixel filters may be optimized to obtain a desiredcombination of a sufficiently wide color gamut, sufficiently highbrightness, and sufficiently high contrast.

For example, the use of more than three primaries in accordance with anembodiment of the invention may enable expansion of the reproduciblecolor gamut by enabling the use of filters with narrower transmissioncurves (e.g., narrower effective transmission ranges) for the R, G and Bcolor filters and, thus, increasing the saturation of the R, G and Bsub-pixels. To compensate for such narrower ranges, in some embodimentsof the invention, broader band sub-pixel filters may be used in additionto the RGB saturated colors, thus increasing the overall brightness ofthe display. In accordance with embodiments of the invention, an optimalcombination of color gamut width and over-all picture brightness can beachieved, to meet the requirements of a given system, by appropriatelydesigning the sub-pixel filters of the n-primary display and the filterarrangement.

FIGS. 5A and 6A schematically illustrate transmission curves for two,respective, alternative designs of a five-primary display device inaccordance with embodiments of the invention, wherein the five primarycolors used are red (R), green (G), blue (B), cyan (C) and yellow (Y),denoted collectively RGBCY. FIGS. 5B and 6B schematically illustrate theresulting color gamut of the filter designs of FIGS. 5A and 6A,respectively. It will be appreciated that both designs produce widergamut coverage and/or higher brightness levels than correspondingconventional three-color LCD devices, as discussed in details below. Asknown in the art, the normalized over-all brightness level of aconventional 3-color LCD may be calculated as follows:Y(3-colors)=(Y(color₁)+Y(color₂)+Y(color₃))/3

Analogously, the normalized brightness level of a 5-color LCD device inaccordance with an embodiment of the present invention may be calculatedas follows:Y(5-colors)=(Y(color₁)+Y(color₂)+Y(color₃)+Y(color₄)+Y(color₅))/5wherein Y(color_(i)) denotes the brightness level of the i'th primarycolor and Y(n-colors) denotes the over-all, normalized, brightness levelof the n-primaries display.

Although the color gamut illustrated in FIG. 5B is comparable with thatof a corresponding 3-color LCD device (FIG. 4B), the brightness levelthat can be obtained using the filter design of FIG. 5A is about 50%higher than that of the corresponding 3-color LCD. The higher brightnesslevels achieved in this embodiment are attributed to the addition ofyellow (Y) and cyan (C) color sub-pixels, which are specificallydesigned to have broad transmission regions and, thus, transmit more ofthe back-illumination than the RGB filters. This new filter selectioncriterion is conceptually different from the conventional selectioncriteria of primary color filters, which are typically designed to havenarrow transmission ranges. The white point chromaticity coordinates forthis embodiment, as calculated from the transmission spectra and theback-illumination spectra using methods known in the known art, arex=0.318; y=0.352.

As shown in FIG. 6B, the color gamut for the filter design of FIG. 6A isconsiderably wider than that of the corresponding conventional 3-colorLCD (FIG. 4B), even wider than a corresponding NTSC gamut, which is theideal reference gamut for color CRT devices, with brightness levelsroughly equal to those of a conventional 3-color LCD. In thisembodiment, the over-all brightness level of the 5-color LCD device issimilar to that of a 3-color LCD device having a much narrower colorgamut.

The white point coordinates for this embodiment, as calculated from thetransmission spectra and the back-illumination spectra using methodsknown in the known art, are x=0.310; y=0.343. Other designs may be usedin embodiments of the invention, including the use of differentprimaries and/or additional primaries (e.g., 6 color displays), toproduce higher or lower brightness levels, a wider or narrower colorgamut, or any desired combination of brightness level and color gamut,as may be suitable for specific applications.

FIG. 7A schematically illustrates filter transmission curves of asix-primary display according to embodiments of the present invention,wherein the six primary colors are red, green, blue, cyan, magenta (M)and yellow, denoted collectively RGBCMY. FIG. 7B schematicallyillustrates the resulting color gamut of the filter design of FIG. 7A.The filter design of FIGS. 7A and 7B is generally similar to that ofFIG. 5A and 5B, except for the addition of a magenta (M) filtersub-pixel to each pixel. The white point coordinates for this exemplarysix-primaries display are x=0.319 and y=0.321 and the brightness gain isequal to one.

FIG. 15 schematically illustrates a chromaticity diagram of the colorgamut discernible by humans, divided into six sub-gamut regions, namelyred (R), green (G), blue (B), yellow (Y), magenta (M) and cyan (C) colorsub-gamut regions, that may be used for selecting effective colorfilters spectra in accordance with embodiments of the invention. In someembodiments, more than three primary color filters, for example, fivecolor filters as in the embodiments of FIGS. 5A and 6A, or six colorfilters as in the embodiment of FIG. 7A, may be selected to producechromaticity values within respective sub-gamut regions in FIG. 15. Theexact chromaticity position selected for a given primary color within arespective sub-gamut region may be determined in accordance withspecific system requirements, for example, the desired width of thecolor gamut in the chromaticity plane and the desired image brightness.As discussed in detail above, the system requirements depend on thespecific device application, e.g., certain applications give preferenceto gamut size, while other applications give preference to imagebrightness. The sub-gamut regions in FIG. 15 represent approximatedboundaries from which primary colors may be selected to provide largegamut coverage and/or high brightness levels, while maintaining adesired white point balance, in accordance with embodiments of theinvention. The positions of the primary chromaticity values within thesub-gamut regions of FIG. 15, for given filter spectra selections andknown back-illumination spectra, can be calculated using straightforwardmathematical calculations, as are known in the art, to determine whethera desired color gamut is obtained for the given filter spectraselections.

In an embodiment of the invention, a sub-pixel rendering technique asdescribed in detail below may be used, in conjunction with the exemplary6-primary design described above, to significantly increase theresolution of the display. In alternate embodiments of the invention,different primaries and primary spectra designs may be used to producedesired results, in accordance with specific display applications.

In some embodiments of the device, system and method of the invention,more than three primaries can be displayed using a format compatiblewith a conventional 3-sub-pixel display format. As known in the art,each pixel of conventional RGB-based LCD devices is composed of threesub-pixels, namely red, green and blue. Typically, each sub-pixel has anaspect ratio of approximately 1:3, whereby the resultant pixel aspectratio is approximately 1:1. The aspect ratio of an image is defined asthe ratio of the number of pixels in a row to the number of pixels in acolumn. The image aspect ratio of a typical full-screen LCD display isapproximately 4:3. The display resolution is determined by the totalnumber of pixels, assuming the pixels are generally square and arrangedin a 4:3 aspect ratio configuration. When displaying a video or graphicimage of a given resolution in a window (e.g., a display pixelarrangement) of another resolution, a scaling function may be required.The scaling function may include interpolation or decimation of theoriginal image pixel data to produce the correct number and arrangementof pixels suitable for a given screen size at the desired displayresolution. For most applications, an overall pixel aspect ratio ofapproximately 1:1 is required. For general video and TV applications,reproducing an exact aspect ratio is not critical. In otherapplications, particularly in applications that require geometricalaccuracy, for example, in displaying images for graphic softwareapplications, such as Adobe PhotoShop®, software rendering methods mayadditionally be used to compensate for pixel size “distortions”.

There are many possible ways of arranging the sub-pixels of amore-than-three-primaries device in accordance with embodiments of theinvention, as described below, such that a pixel aspect ratio ofapproximately 1:1 would be maintained. The over-all resolution and theaspect ratio of an LCD device are generally determined at the hardwarelevel, e.g., by the number of LC cells in the LC array of the device.Although it is possible to change the geometric design of an existingLCD device, for example, to design a new sub-pixel layout with asub-pixel aspect ratio other than 1:3, such design change may beexpensive and thus undesirable. Therefore, in some embodiments ofinvention, a conventional sub-pixel aspect ratio of 1:3 may bemaintained by arranging the sub-pixels in efficient configurations asdescribed below. Such configurations may have an aspect ratio as closeas possible to 1:1, and the configurations may include periodic patternsof more-than-three sub-pixel filters that can be illuminated bycorresponding cells of the LC arrays used in standard RGB displays,obviating the need to design a new type of display, e.g., a new TFTactive matrix design. The option of integrating the features of thepresent invention into existing display designs is a significantadvantage of embodiments of the invention, because re-designing of basicdisplay components, particularly designing a new type of TFT activematrix, may be extremely complicated and costly.

The periodic sub-pixel patterns mentioned above, hereinafter referred toas “super-pixel” structures, may contain several color sub-pixels, forexample, at least one sub-pixel for each of the more-than-threeprimaries. As discussed above, to avoid redesigning of basic displaycomponents, the super-pixel structures may be designed to fit existingRGB sub-pixel array formats. Assuming a rectangular super-pixelstructure, in accordance with some embodiments of the invention, eachsuper-pixel may include m×k sub-pixels, whereby the number of n-primarypixels (n>3) in the super-pixel structure is equal to (m×k)/n. Becausethe number of n-primary pixels in the “super-pixel” structure is alsoequal to N_(L)×N_(W), wherein N_(L) and N_(W) are the length and widthof the super-pixels, measured in n-primary pixel units, the followingequation holds:N _(L) ×N _(W)=(m×k)/n

The length of the super-pixel structure is N_(L)×L, which is equal tom/3, and the width of the super-pixel is N_(W)×W, which is equal to k,wherein L and W are the average length and average width, respectively,of an n-primary pixel, measured in three-cell pixel units. Therefore,the average aspect ratio of the n-primary pixels is given by:L/W=m/(3k)×N _(W) /N _(L) =m ²/(3n)N _(L) ⁻²

To determine the smallest super-pixel structure that meets the aboverequirements, the number of n-primary pixels lengthwise or widthwise ineach super-pixel is set to a value of one, for example, N_(L)=1, wherebythe aspect ratio of the multi-primary pixel is given by m²/3n.Therefore, the smallest super-pixel structure would be obtained for avalue of m whereby m² divided by 3n is as close as possible to one.

For example, a straightforward configuration for a 4-primaries display,such as a RGBY (RGB+Yellow) display system in accordance with theinvention, may include arranging the sub-pixels side by side in astructure that maintains an overall image aspect ratio of 4:3, as shownschematically in FIG. 8. This configuration yields a value of m=4. Inthis configuration, for example, using an LC array designed for an XGAdisplay with a 3-primary pixel resolution of 1024×768, yields aneffective resolution of 768×768 in the 4-primary multi-pixelconfiguration described above. Similarly, a SXGA panel with a 3-primarypixel resolution of 1280×1024 can be adapted in accordance with thisembodiment of the invention to reproduce 4-primary color images at aresolution of 960×1024 pixels. It should be appreciated that the4-primary pixel shape in accordance with this embodiment is rectangularand not square and, therefore, the image aspect ratio remains unchangedwhen data scaling is applied. In the embodiment of FIG. 8, the aspectratio of the 4-primary pixels is 4:3. Therefore, for example, an XGAscreen according to this embodiment of the invention may have an equalnumber of n-primary pixels lengthwise and widthwise and, thus, the imageaspect ratio for such XGA screen remains 4:3. However, the horizontal(row) resolution of such a screen would be lower in comparison to acorresponding 3-primary XGA screen. In an embodiment of the invention,to maintain correct image geometry of this 4-primary display, thehorizontal resolution of the original input data, e.g., 1024 for XGAscreen, is reduced proportionally, e.g., to 768 for XGA screen. It willbe appreciated by persons skilled in the art that other display formatsmay require different adjustments. For example, SXGA screens, at aresolution of 1280:1024, have a 5:4 aspect ratio, rather than 4:3, in3-primaries format.

FIG. 9 schematically illustrates another example of a super-pixelconfiguration in a 5-primaries display system in accordance with anembodiment of the invention. In this 5-primaries configuration, wherein,for example, the primaries are RGB, cyan (C) and yellow (Y), a value ofm=4 yields a 5-primary pixel aspect ratio of 16:15. In the super-pixelconfiguration of FIG. 9, for each pixel, the 5 sub-pixels may bedivided, for example, across two consecutive rows, and the super-pixelstructure includes four sets of 5-primary pixels. The aspect ratio foreach super-pixel is 15:4 and, thus, the effective aspect ratio of asingle 5-primary pixel is 16:15. In this configuration, for example, anLC array designed for an XGA display with a 3-primary pixel resolutionof 1024×768, yields an effective 5-primary pixel resolution of 768×614.Similarly, a SXGA panel with a 3-primary pixel resolution of 1280×1024can be adapted, in accordance with this embodiment of the invention, toreproduce 5-primary color pixel resolution of 960×819.

It should be noted that, in the above examples, the effective(color-weighted) centers of the multi-primary pixels may shifthorizontally and/or vertically. This should be taken into account wheninput data is interpolated to match the structure of the pixel. Theperiodic structure of the super-pixel configuration described aboveallows a relatively simple interpolation process, as follows. The datafor each super-pixel may be first calculated as a position on arectangular grid of super-pixels; then the data is distributedinternally within each super-pixel. Since the internal structure of thesuper-pixel is fixed, e.g., all super-pixels have the same sub-pixelstructure, the internal distribution stage is also fixed, e.g., internaldistribution is performed in the same manner regardless of the positionof each super-pixel on the display. Thus, the interpolation process canbe performed on a simple rectangular grid, and the complex distributionassociated with the internal super-pixel structure is reduced to afixed, repetitive, operation. Other suitable interpolation methods mayalso be used in conjunction with the invention.

A system that performs an interpolation process as described above isillustrated schematically in FIG. 11. The input data at the originalresolution (e.g., in YCC or RGB format) is received by an image scalingunit 1102, which scales the image resolution, defined by the number ofpixels in the image, to the resolution of the display. The scaling maybe similar to the scaling performed on a personal computer (PC) withvarying display resolution, as is known in the art. The data may beup-scaled to a much higher resolution and then re-sampled to the displayresolution, as explained, for example, in Keith Jack, “VideoDemystified”, 3^(rd) Edition, LLH Technology Publishing, 2001.Optionally, following the up scaling, re-sampling may be performed intwo stages, to simplify computation, as follows. In a first stage, datais allocated for each of the super-pixels. In a second stage,re-sampling is performed at the super-pixel level, based on the knownstructure of the super-pixels. After the data is re-sampled to ann-primary pixel grid, which may be defined, for example, by thecolor-weighted centers of each of the n-primary pixels, a set ofn-primary coefficients may be computed for each of the n-primary pixelsby an n-primary converter 1104. The n-primary data for all, e.g., m,n-primary pixels making-up each of the super-pixels is combined by asuper-pixel collector 1106, and the collected data is received by adistributor 1108, which distributes the m*n coefficients of the mn-primary pixels to the sub-pixels according to the defined internalarrangement.

In a 6-primaries display system according to an embodiment of theinvention, one possible configuration may include a super-pixelarrangement essentially analogous to the 5-primaries super-pixelarrangement described above with reference to FIG. 9, with appropriatechanges, e.g., adding a magenta sub-pixel element to each pixel of thesuper-pixel structure. A system for producing 6-primary images inaccordance with this embodiment, and the flow of data in such a system,may be substantially as described above with reference to FIG. 11. Asillustrated schematically in FIG. 10, a super-pixel structure with n=6and m=4 has a length 4/3 that of a 3-primary pixel, and a width of 3pixels. The total number of sub-pixels in this super-pixel structure isthus 4/3×3×3=12, whereby two 6-primary pixels are accommodated by eachsuper-pixel, as illustrated schematically by the shadowed area in FIG.10. The average length of this 6-primary pixel is 4/3 and its width is3/2 and thus the super-pixel aspect ratio in this embodiment is 8:9,which is relatively close to the desired 1:1 ratio.

Other configurations may also be used in accordance with embodiments ofthe invention; for example, the six sub-pixels may be arranged in tworows of three sub-pixels each. In this two-row arrangement, theresolution of a standard XGA display adapted to operate in asix-primaries mode according to the invention is reduced 1024×384pixels, and the resolution of a standard SXGA display operating in the6-primaries mode is reduced to 1280×512. Such a configuration of pixelsmay be useful for TV and video applications as described below.

The above examples demonstrate that an increase in the number ofdifferent color filters, e.g., 4-6 different colors instead of 3,without appropriate modification of the LC array, may reduce theapparent resolution of the display. However, for TV and videoapplications this reduction in apparent resolution may not be crucial.Standard definition NTSC TV systems have a resolution of 480 lines(effectively 525 lines with blanking lines) at an interlaced field rateof 60 Hz (frame rate of 30 Hz). When digitized, the resolution of NTSCsystems varies within the range of 960×480 to 352×480. PAL systems havea resolution of 576 TV lines at an interlaced field rate of 50 Hz (framerate of 25 Hz). In digital form, the resolution of PAL systems varieswithin the range of 1024×576 to 480×576, depending on the aspect ratio(e.g., 4:3 or 16:9) and on the shape (e.g., rectangular or square) ofthe pixels. Therefore, in accordance with embodiments of the invention,existing SXGA displays can be converted into four-, five- orsix-primaries display systems, as described above, that display standarddefinition TV images without any degradation in image resolution,because the reduced resolution of such converted devices is still higherthan the resolution of standard TV image data. It should be noted thatin all the cases described above, where the resolution is reducedhorizontally, and in the case of five- and six-primaries where theresolution is reduced vertically, the resolution of converted displaysystems in accordance with embodiments of the invention are compatiblewith (or exceed) the resolution of NTSC systems (480 lines) and are atleast very close to the resolution of PAL systems (576 lines). Incertain cases where an XGA display is converted to operate as a 4-6primary display, some resolution may be lost; however, a sophisticatedarrangement of the sub-pixels within each pixel, as described below, canbe used to compensate for the slightly decreased resolution. Thus, itwill be apparent to a person skilled in the art that many existing typesof 3-color LCD devices can be converted into more-than-three-primarydisplays, according to embodiments of the invention, capable ofdisplaying TV standard images with no effective reduction in resolution.Other resolutions, number of primaries and pixel arrangements may beused in accordance with embodiments of the invention.

In various applications, especially in mixed video and computer graphicsapplications, any loss of resolution should preferably be avoided. Forpixels with six sub-pixels arranged in two rows, as described above,special arrangement of the different sub-pixel colors can be implementedto improve the display resolution. An example of such an arrangement isshown in FIG. 12A. In this arrangement, the sub-pixels in each pixel arearranged in two rows, each row including three sub-pixels. Row Acontains the “saturated” RGB pixels, and row B contains the “bright” CMYpixels. The CMY pixels combination can also produce less saturated RGBcolors, for example, colors that are included in the triangular colorgamut defined by the chromaticity values of C, M and Y. Analyzing thisstructure column-wise, each vertical sub-pixel pair can individuallyreproduce white (e.g., neutral) chromaticity, as follows: R+C; G+M; orB+Y. This is achieved by arranging the sub-pixels such that each primarycolor sub-pixel is positioned vertically adjacent a complementaryprimary color sub-pixel. Thus, using this method, the horizontalBlack/White resolution for graphics applications can be increased by afactor of three.

FIG. 12B depicts another exemplary arrangement of display pixels inaccordance with embodiments of the invention. While in the arrangementof FIG. 12A, row A contains only RGB sub-pixels, and row B contains onlyCMY sub-pixels, in the alternative arrangement of FIG. 12B both RGB andCMY pixels are included in each row. More specifically, as shown in FIG.12B, row A contains the RGB sub-pixels of a first pixel followed by theCMY sub-pixels of a second pixel, and row B contains the CMY sub-pixelsof the first pixel followed by the RGB pixels of the second pixel. Itshould be appreciated that various other pixel arrangements may also besuitable for designing super-pixel structures in accordance withembodiments of the invention; for example, in some embodiments, theorder of primary colors within each triad of primaries may be differentfrom the orders shown in the accompanying drawings.

The 6-primary arrangement described above allows for at least threemodes of operation of a 6-primary display in accordance with theinvention. FIG. 13A schematically illustrates the color gamut of such a6-primary display on a chromaticity plane. The full color gamut isrepresented by the dotted line connecting the six primaries. The gamutof the RGB primaries alone is represented by the dashed triangle, andthe gamut of the CMY primaries spans the solid triangle. The shadowedhexagonal area in FIG. 13A represents the conjunctive gamut of both theCMY and RGB primary sets. A first mode of operation of this display is ahigh resolution, “limited gamut” mode, which is suitable, inter alia,for graphics applications. In this mode, the resolution can be the sameas that of a corresponding 3-primary display (e.g. 1280×1024 pixels forSXGA displays; 1024×768 for XGA displays; etc.) The color combinationsfor this type of arrangement can be produced by both the RGB and CMYtriads (sub-structures), whereby the color gamut of the display isdefined by the conjunction of the CMY color gamut and the RGB colorgamut, e.g., the shadowed hexagon in FIG. 13A. In this mode ofoperation, colors are handled at the three-sub-pixels level, e.g., datasuitable for driving a 3-primary color display is delivered to eachpixel, regardless of the set of primaries allocated to the pixel, e.g.,RGB or a CMY. The difference between the RGB and the CMY pixels is inthe matrix that converts the input data into the coefficients used todrive the sub-pixels. More elaborate data flows are also possible, andwill be presented below.

A second mode of operation of a 6-primary display in accordance withembodiments of the invention is a medium resolution, super-wide gamutmode, designed, e.g., for video and other display applications requiringrich colors and improved color picture quality. In this mode, theresolution may gradually decrease from normal, suitable for“non-saturated color objects”, that will be displayed at the full systemresolution (e.g., 1280×1024 pixels for SXGA displays) to that ofextremely colored “very saturated color objects” where resolution willdecrease by a factor of two (1280×512 pixels). In this mode, color ishandled at the six-primary pixel level and, therefore, the displayresolution may be reduced. However, if the colors to be presented arenot saturated, e.g., if the colors being displayed are included in theshadowed hexagon in FIG. 13A, such colors may be properly reproduced byeither a RGB pixels or the CMY pixels and, therefore, the originalresolution may be restored. For saturated colors outside the shadowedare in FIG. 13A, the resolution is reduced by a factor of two (1280×512pixels); however, full resolution is not typically required for highlysaturated colors because the human visual system is more sensitive tospatial variations in brightness than to spatial variations in color.

A third mode of operation of a 6-primary display in accordance with anembodiment of the invention is a super-high resolution mode, which maybe used for black-and-white graphics, for example, using a SXGA display,yielding an effective resolution of 3840×1024 pixels, instead of theoriginal 1280×1024 resolution. The arrangement and handling of thepixels for this mode of operation may be as in the high resolution,“limited gamut” mode described above. Additional modes of operation arealso possible in accordance with embodiments of the invention; suchadditional modes may be designed in accordance with specific displayrequirements.

FIG. 13B schematically illustrates possible data flow schemes for a6-primary display system in accordance with exemplary embodiments of theinvention, using RGB-CMY primary color sets as described above. In thisexample, the resolution of the input data is assumed to be at theoriginal resolution of the display; otherwise, appropriate scaling maybe required as described above. A pixel collector 1302 collects imagedata corresponding to a pair of three-primary pixels, namely, a RGBpixel and a CMY pixel, which together form a single 6-primary pixel. Theoriginal image data may be provided in any suitable format known in theart, for example, RGB or YCC format. Using matrix multiplication units1304 and 1306 and, subsequently, an n-primary combiner 1308, thecollected data of the two three-color pixels is converted intogray-scale values for the different sub-pixels. If the color values ofboth pixels fall within the shadowed hexagonal area in FIG. 13A, e.g.,if all the sub-pixels have positive gray scale values, then the graylevels used to drive the respective LC sub-pixels are unchanged.

Referring to FIG. 13A, when the input data falls outside the CMYtriangle but within the RGB triangle, the data may be handled in anumber of different manners, depending on the specific application. Inone embodiment, the data is represented only by the RGB sub-pixelcomponent, and the CMY component is set to zero illumination. In anotherembodiment, the input data is represented by the RGB component, and theCMY component represents the color combination nearest the desiredcolor. For the purpose of this embodiment of the invention, the“nearest” color combination may be defined in terms of brightness,chromaticity, or simply by setting any negative sub-pixel values tozero. In a further embodiment, the CMY component represents the colorcombination nearest as possible to the desired color, and any differencebetween the desired color and the CMY representation is corrected by theRGB component. The three different embodiments discussed above differmainly in the method of presenting saturated colors. In the firstembodiment, saturated colors are reproduced accurately, fromcolorimetric point of view, but at a relatively low brightness level. Inthe second embodiment, the brightness level is maximized, but saturationis decreased. In the third embodiment, the saturation and brightnesslevel fall within the range in between the maximum and minimum levels ofthe first and second embodiments. It should be appreciated that, bytransposing the references to CMY and RGB, respectively, in the aboveanalysis, the same analysis applies to a situation in which the inputdata falls outside the RGB triangle but within the CMY triangle in FIG.13A.

Referring to FIG. 13A, it should be noted that any color combinationwithin the 6-color gamut (the peripheral dotted hexagon) that fallsoutside the “star of David” shape formed by the conjoined triangularareas of the RGB gamut and CMY gamut, can be reproduced accurately onlyby the full six-primary pixel representation. In an embodiment of theinvention, an algorithm using two-dimensional look-up-tables (“LUTs”),as described in Applicants' pending International ApplicationPCT/IL02/00410, filed May 23, 2002, entitled “System and method of dataconversion for wide gamut displays”, the disclosure of which isincorporated herein by reference, may be applied to derive the correctsub-pixel values for all six primaries in real time. In this embodimentof the invention, the average color of the RGB and the CMY combinationsmay be calculated, and the resulting color may be transformed, e.g.,using a six-primary converter, to produce the sub-pixel coefficients ofthe corresponding n-primary pixel.

The systems and methods described above are suitable for display devicesin which colors are perceived by spatial integration of the sub-pixelsby the human vision system. However, color integration by the humanvision system can also be performed temporally and, therefore,embodiments of the present invention also provide sequential displaydevices, systems and methods, for example, sequential color LCD devices,using more than three primary colors. This concept is described indetail, in the context of sequential n-primary color image projectiondevices, in Applicants' International Application PCT/IL01/00527,entitled “Device, System and Method For Electronic True Color Display”,filed Jun. 7, 2001, and published Dec. 13, 2001 as WO 01/95544, theentire disclosure of which is incorporated herein by reference. Insequential projection color displays devices, four or more differentcolor fields are projected sequentially, each for a short time period,and the process is repeated periodically at a sufficiently highfrequency, whereby the human vision system temporally integrates thedifferent color fields into a full color image.

An advantage of LCD devices based on sequential color representation, inaccordance with embodiments of the present invention, is that suchdevices can display more-than-three-primary color images at a resolutioncomparable to the resolution at which the same devices can displaythree-primary-color, e.g., RGB, images. Sequential LCD display devicesdo not require a color sub-pixel filter matrix in registry with the LCarray. Instead, each LC element controls the intensity of all theprimary colors for a given pixel, each primary color being controlledduring designated time slots, whereby the LC array is utilized to itsfull resolution. Color combinations are created by sequentiallyback-illuminating the LC array with different primary colors, in analogyto sequential projection devices. However, in contrast to projectiondevices, which typically require significant physical space to containthe projection optics, namely, the optical setup that projects aminiature spatial light modulator onto a screen, the sequential LCDdevice of the present invention does not require projection optics andmay, thus, be implemented in flat configurations.

The architecture of a flat n-primaries display according to anembodiment of the present invention includes an LC array (panel) havinga desired size and resolution. Such LCD panels are used, for example, inportable computers as are known in the art. However, in the sequentialLCD devices of the present invention, the LC panel may be used withoutan adjacent array of color sub-pixel filters, whereby the LC array mayoperate as a monochromatic gray level device. The cells of the LC arrayare selectively attenuated to produce a series of more-than-threeprimary gray-level patterns, each pattern corresponding to one ofmore-than-three primary color components of the displayed image. Eachgray-level pattern is back-illuminated with light of the correspondingprimary color. Switching among the different back-illuminations colorsis synchronized with the sequence of gray-level patterns produced by theLC array, whereby each gray level pattern in the sequence is illuminatedwith light of the correct primary color. The light for the desiredback-illumination may be produced by filtering white light (or othercolor light) through pre-selected color filters, each filtercorresponding to one of the more-than-three primary colors. Theback-illumination color sequence is repeated at a sufficiently highfrequency, synchronized with the periodic sequence of patterns producedby the LC array, whereby the viewer perceives a fill color image bytemporal integration of the as described above.

Parts of a sequential LCD device in accordance with an embodiment of theinvention are schematically illustrated in FIG. 14. It should beappreciated that the sequential color LCD devices described hereinillustrate only an exemplary embodiment of the invention. In alternateembodiments of the invention, other systems and methods may be used tocreate the different colors of back-illumination light. Additionally oralternatively, in some embodiments of the invention, instead of using anLC array as described above, other methods known in the art may be usedto sequentially produce the gray level patterns corresponding to thedifferent primary color components.

In one embodiment of the invention, illustrated schematically in FIG.14, the different illumination colors are produced sequentially, using asingle light source, or a set of light sources, for example, a whitelight source 1410, by sequentially filtering the white light through aseries of different color filters 1413. The color filters may be placedon a rotating filter wheel 1412. To obtain the desiredback-illumination, the colored light passing through one of colorfilters 1413 on filter wheel 1412 may be focused, e.g., using a lens1414, into a light guide 1416. The light guide funnels the filteredlight to a back-illumination arrangement 1422 juxtaposed an LC array1420, as known in the art, illuminating the LC array substantiallyuniformly. In some variations of this embodiment, the back-illuminationarrangement and light guide are similar to those used inback-illuminated portable computers, e.g., laptop computers, or inlight-table devices. In some such devices, light from fluorescent lightbulbs is reflected by an arrangement of reflectors/diffusers to obtainsubstantially uniform illumination. Alternatively, as shownschematically in FIG. 14, the light funnel 1416 may include multiplelight exits 1418 that may be used in conjunction withreflectors/diffusers in back-illumination arrangement 1422 to obtainuniform illumination. In alternate embodiments other structures may beused to provide back-illumination of different primary colors.

In alternate embodiments of the invention, the back-illumination isgenerated by an array of Light Emitting Diodes (LEDs), each LED capableof selectively producing light at one of more than three differentwavelength ranges. The different color LED emissions are activatedsequentially, and the color sequence is synchronized with the sequenceof gray-level patterns produced by the LC array. In a three-primary,e.g., RGB, device using LED back-illumination, in order to obtain asufficiently wide color gamut, the red, green and blue LED emissions aretypically designed to have narrow respective spectra. In particular, thepeals of the emission distribution of such devices is typically in therange of 630-680 nm for the red emission, 500-540 nm for the greenemission, and 400-480 nm for the blue emission. Unfortunately, existingthree-color devices do not utilize the brightness-efficient wavelengthrange of 540-570 nm, perceived as orange-yellow light, at whichwavelength range the human eye is most sensitive. Therefore, adding afourth LED emission in the range of 540-570 nm, in accordance withembodiments of the invention, can significantly improve the brightnessefficiency. Assuming that the quantum efficiency of all diodes issubstantially the same, a yellow LED would produce more visualbrightness per Ampere. To take advantage of this efficiency, byactivating the four LED emission ranges described above, in someembodiments of the invention, at least four primary colors, namely, red,green, blue and yellow-orange, are used.

In an alternative embodiment of the invention, instead of using a fourthemission range, an array of standard RGB LEDs may be activated inaccordance with an activation sequence that produces a higher intensityof the desired back-illumination sequence. Instead of the standardactivation sequence of R-G-B-R-G-B, some embodiments of the inventionuse a hybrid periodic activation sequence, for example, R-G-B-RG-BG-RB,to produce the desired back-illumination sequence. Other activationsequences of the RGB LED emissions are also possible, for example,sequences including the same emission components (e.g., R, G, B, RG, BGand RB) arranged in different orders, sequences in which some of the“mixed” components (e.g., RG, BG, or RB) are omitted, sequencesincluding additional components (e.g., a full RGB emission component),or any other suitable combinations of “pure” and/or “mixed” LEDemissions capable of produce the desired back-illumination sequence. Itshould be appreciated that the over-all brightness level produced by theexemplary activation sequence of R-G-B-RG-BG-RB, determined by the sum3R+3G+3B, is about 50 percent higher than the average brightnessproduced by a corresponding standard R-G-B-R-G-B sequence, determined bythe sum 2R+2G+2B.

The sequential LCD device in accordance with embodiments of theinvention is activated at a sufficiently high frequency to enable aviewer to temporally integrate the sequence of n-primary images into afull color image. Additionally, to produce a video image, the sequentialLCD device in accordance with embodiments of the invention is activatedat a sufficiently high rate to enable reproduction of the requirednumber of frames per second. A sequential color LCD device that operatesat a sufficiently fast rate, using back-illumination of three primarycolors, namely, red, green a blue light, is described in Ken-ichiTakatori, Hiroshi Imai, Hideki Asada and Masao Imai, “Field-SequentialSmectic LCD with TFT Pixel Amplifier”, Functional Devices Research Labs,NEC Corp., Kawasaki, Kanagawa 216-8555, Japan, SID 01 Digest,incorporated herein by reference. In an embodiment of the presentinvention, a version of this three-color device is adapted to producen-primary color images, wherein n is greater than three. In suchn-primary-adapted sequential illumination device, light generated by a(preferably) white light source is filtered through n, sequentiallyinterposed, color filters, to produce the desired sequence of n-primarycolor back-illumination. A filter switching mechanism, for example, arotating filter wheel including more than three different color filters,such as the filter wheel described above with reference to FIG. 14, maybe used to sequentially interpose the different color filters in lightpath of the back-illumination. An arrangement similar to that used inexisting laptop computers may be used to funnel and diffuse the filteredlight illuminating the LC array. In some embodiments, the light sourceand filter switching mechanism (or, alternatively, the array of LEDsdescribed above) are housed in an external device, and a light guide isused to funnel colored light into the back-illumination arrangement ofthe LCD device, as described above with reference to the embodiment ofFIG. 14.

It will be appreciated by persons skilled in the art that the presentinvention is not limited by what has been particularly shown anddescribed hereinabove and with reference to the accompanying drawings.Rather, the invention is limited only by the following claims.

1. A color Liquid Crystal Display (LCD) device for displaying a colorimage using at least five different colors, the device comprising: anarray of Liquid Crystal (LC) elements; driving circuitry adapted toreceive an input corresponding to said color image and to selectivelyactivate the LC elements of said LC array to produce an attenuationpattern corresponding to a gray-level representation of said colorimage; a back illumination source to generate light; and an array ofcolor sub-pixel filter elements to filter the light generated by saidback illumination source, said array of color sub-pixel filter elementsbeing juxtaposed and in registry with said array of LC elements suchthat each color sub-pixel filter element is in registry with one of saidLC elements, wherein said array of color sub-pixel filter elementscomprises at least five different colored sub-pixel filter elements,which transmit light of said at least five different colors,respectively, wherein the light transmitted through each of saidsub-pixel filter elements is independent of the other sub-pixel filterelements, and wherein the color gamut of the LCD device is wider thanthe color gamut of a standard RGB display.
 2. A device according toclaim 1, wherein said at least five colors comprise red, green, blue,and yellow.
 3. A device according to claim 2 wherein said at least fivecolors further comprise cyan.
 4. A device according to claim 1 whereinsaid device displays said color image using at least six differentcolors, and wherein said types of color sub-pixel filter elementscomprise at least six types of color sub-pixel filter elements, whichtransmit light of said at least six colors, respectively.
 5. A deviceaccording to claim 4 wherein said at least six colors comprise red,green, blue, yellow and cyan.
 6. A device according to claim 5 whereinsaid at least six colors further comprise magenta.
 7. A device accordingto claim 1, wherein the wavelength ranges of said at least four colorsare selected to provide an optimal over-all brightness.
 8. A deviceaccording to claim 1, wherein the wavelength ranges of said at leastfour colors are selected to provide an optimal color gamut width of thedisplayed images.
 9. A device according to claim 1, comprising acontroller to receive data representing said color image in terms ofthree data components, and to provide said driving circuitry with saidinput representing said color image in terms of said at least fourcolors.
 10. A device according to claim 1, wherein the color gamut ofthe LCD device includes the entire color gamut of said standard RGBdisplay.
 11. A device according to claim 1, wherein the color gamut ofthe LCD device is wider than NTSC standard color gamut.
 12. A deviceaccording to claim 3 wherein each of said red, green and blue filterelements has narrower transmission bandwidth than each of said yellowand cyan filter elements.
 13. The device according to claim 2, whereineach of the five different colored sub-pixel filter elements has atransmission bandwidth independent of the other four sub-pixel filterelements.
 14. The device according to claim 1, wherein each sub-pixelelement is adjacent on a first axis to two different colored sub-pixels,and wherein each sub-filter element is adjacent on a second axisorthogonal to said first axis to two sub-pixels each having the samecolor as said sub-pixel element.
 15. The device according to claim 1,wherein each row contains repetitions of said at least four sub-pixels,and wherein each row is a shifted copy of an adjacent row.
 16. Thedevice according to claim 1, wherein each sub-pixel has aspect ratio of1:3, thereby resulting in three adjacent sub-pixels having an aspectratio of substantially 1:1.